The present invention relates to a map distribution server for automotive navigation systems, a map data distribution system, and a road difference data production method. More particularly, the present invention is concerned with a production system and method for automotive navigation systems for producing difference update data in compliance with addition of a new road or modification or deletion of an attribute of an existing road.
In automotive navigation systems, a map is displayed on a screen in order to support a user's designating a destination or a route or to assist a user in finding a vehicle moving route to a designated destination. Thus, an automotive navigation map is used for various purposes. Map data for the automotive navigation system is preserved in the form of a database in a storage medium. Information on a road newly constructed after the storage medium is manufactured or information on modification or deletion of an attribute of an existing road has to be updated from time to time. As one means for making such update data of the automotive navigation system map available to a user, there is a method of utilizing a service which an automotive navigation map provision vendor renders over a communication network.
Patent documents 1 to 3 (Japanese Unexamined Patent Application Publications Nos. 2008-90195 and 2007-241003, and Written Opinion (WO) No. 2006/011278 A1) have disclosed distribution systems for map update data to be organized by such automotive map provision vendors.
According to a map data distribution system described in the patent document 1, those out of plural link data items to be updated, which are interconnected as a network, are managed as one map update data. If updating map data of a designated area is requested, the map data is updated with map update data that is at least partly concerned with the area. Accordingly, while the connectivity of the updated road network is guaranteed, a data size to be communicated for updating can be decreased.
According to a map updating system described in the patent document 2, if updating map data of a designated area is requested, difference update data of the designated area and update data on which the difference update data depends are specified. The data items are updated in chronological order. Accordingly, while an amount of update data is suppressed, map data of a desired area can be updated to the latest, and the consistency of the designated area with an adjoining area whose data is not updated can be sustained.
According to a map data distribution system described in the patent document 3, information on a date when link data is updated, and information on a range which is affected by the updating are preserved in a server in relation to each link. If a terminal requests updating of map data of a designated area, the server transmits links in the area to the terminal, and also transmits to the terminal data of a link, which has been updated after a previous updating request is issued, out of links that are affected by the updating of the links in the area. Accordingly, occurrence of unnecessary communication traffic can be suppressed, and map data can be updated so as not to bring about an inconsistency in an updated map.